Cleaton, H-frames will be an excellent choice. Built the MJK-way and crossed 2nd order they will, as you learn on Martin's web, also be perfectly equalised for flat performance.
Just to choose crossover- frequency to mix with the other speaker. However I would suggest that Beta15 might be better sonically than the Alpha15. The 1 watt sensitivity will be 86 dB for a Beta unit in the proposed H-frame and the bass wll go down to about 30 Hz no doubt.
/Erling